In the past, the most frequently used methods in painting metallic articles having irregularly shaped surfaces have included hand or automatic spray painting, electrostatic painting, brushing, or dipping. Electrophoretic techniques have been utilized in coating articles having a relatively small surface area, but these techniques have been restricted to the application of special coating materials. The present methods of applying a surface coating on large metallic articles have resulted in the waste of relatively large amounts of the coating due to overspraying or due to the accumulation of excess paint material along certain surfaces of the coated articles. Additionally, these coating techniques have usually resulted in a relatively poor surface finish to the article being coated due to uneven distribution of paint or due to surface blemishes. Additionally, prior methods for applying a coating onto comparatively large metal articles has been the fact that it is rather difficult to obtain a relatively uniform film of paint over the entire surface of the metal articles. Also, generally many of the metal surfaces are not readily accessible to the application of the coating material which results in an unsatisfactory or spotty coating. Recessed areas such as the rocker panels of automobiles have only been coated by the prior art techniques at considerable expense because of the requirements of special coating techniques or special hand labor operations in order to obtain at least a minimum measure of protective coating against corrosion. The technique of dipping the metallic article in a paint bath to obtain a coating on recessed surfaces of a metallic article has not proven satisfactory since the evaporation of solvents from the paint film has resulted in the washing off of a portion of the adhered paint coating.
It has been found that a resinous reaction product of a substantially water-insoluble, substantially fully etherified tetramethylol guanamine or a substantially fully etherified hexamethylol melamine reacted with a hydroxy alkylated phenol can be used as a cross-linking agent in an aqueous dispersion of a mixture of said resinous reaction product with a water-dispersible, non-gelled polymeric material carrying an anionic charge, namely, either cationic or anionic charges, which polymeric material is heat reactive with said cross-linking agent, namely the resinous hydroxyl alkylated phenol modified etherified tetramethylol guanamine or hexamethylol melamine compound and such dispersions can be applied to metals by use of an electrodeposition technique.